1. Field of the Invention
The present invention pertains to alternating type plasma panels. It also pertains to methods for the control of these panels.
2. Description of the Prior Art
Alternating-type plasma panels, such as those currently in the market, comprise, as shown schematically in FIG. 1, two glass envelopes 1 and 2, with each envelope bearing an array of electrodes, x.sub.1,x.sub.2,x.sub.3...,y.sub.1,y.sub.2,y.sub.3..., that are parallel to one another and are lined with a dielectric layer 3. The two envelopes are mounted and sealed so that the two electrode arrays are perpendicular to each other, and so that there is a very small distance between the two facing dielectric layers 3. This space between the two dielectric layers is filled with a gas which is generally neon-based. Each pixel is defined by the intersection of two perpendicular electrodes. The display of data is done by the repeated lighting up of a luminescent discharge within the gas, by means of addressing and refresh signals conveyed by the electrodes. The addressing signals are used to create discharges or to eliminate the possibility of subsequent discharges for the selected pixels. The refresh signals are used to create periodic discharges for the pixels that are lit up.
This structure of a plasma panel with two electrodes per pixel has the advantages of technologicial simplicity of construction, sturdiness and the fact that it uses well-known electric control circuits. However, this structure has the following two disadvantages:
there is a large number of electrodes to be connected. Thus, for high-definition screens where it is sought to control 1000 pixels, a minimum of 2000 electrodes have to be connected. Consequently, the connections to be made and the control circuits of these screens are generally more costly than the panel itself;
in practice, it has proved to be difficult, with plasma panels using two electrodes per pixel, to obtain any color other than the conventional orange-red of neon.
For, the obtaining of light of another color, with high luminous efficiency and, even more so, the simultaneous restitution of several colors, requires that one or more layers of luminophores be deposited on the dielectric layers 3, the said luminophores converting the ultra-violet radiation generated by the discharges into visible light. In conventional structures with two electrodes per pixel, problems are raised by the depositing of these luminophores, their positioning with respect to the electrodes and their deterioration caused by the ions present in the discharges.
Plasma panel structures other than the conventional one shown in FIG. 1 have been proposed. None of them has been entirely satisfactory.
For example, we might refer to a panel structure with three electrodes per pixel, described in the European patent 0.135.382. This structure is shown in FIG. 2.
Each pixel is defined by two parallel and coplanar electrodes, X and Y, and by an electrode Z, perpendicular to the other two. In FIG. 2, the three electrodes, X, Y, and Z, are borne by the same glass envelope 1. The dielectric layer 3 insulates the electrodes X and Y from the electrode Z, and also covers the electrode Z. Consequently, the glass envelope 2 bears no electrodes and can, therefore, receive luminophores that emit the desired color or colors by photoluminescence. The addressing signals are applied to the crossed electrodes Z and X or Z and Y, and the refresh signals are applied to the parallel electrodes X and Y. The refreshing is thus done by creating lateral discharges between the two parallel and coplanar electrodes, X and Y.
The European patents, 0.135.382 and 0.157.248, describe methods to control the plasma panels shown in FIG. 2. These methods make it possible to reduce the number of control circuits, but, on the other hand, the number of connections may be increased.
Thus, in the case of a panel with 1024 pixels, depending on the control method used the number of control circuits varies between 64 and 1025 and the number of connections varies between 1056 and 1025.
Furthermore, as in the case of panels with two electrodes per pixel, the control circuits are complicated because the same electrodes, X or Y, are used for both addressing and refreshing and, while the addressing signals are low powered, the refresh signals are high powered.
The present invention pertains to a new alternating type of plasma panel structure.